Videos posted online showed some fans hurling bottles at mounted police in a stand-off in a narrow street.

Dutch police said officers were also attacked with sticks.

But Celtic fans coming home last night blamed the trouble on “heavy-handed” local police.

And other video clips showed fans in the square being attacked by plain-clothes officers.

Celtic said they had received “numerous complaints” about how their fans were treated.

They added that supporters had been “subjected to a high degree of provocation”, and the vast majority of their fans had behaved impeccably.

Dutch police said: “At the end of the afternoon a large group of Celtic supporters attacked police officers in plain clothes.

“Eight were injured and one was knocked unconscious. A few had broken noses and needed stitches above their eyebrows and on their lips. Bottles and sticks were used.”

Inspector Rob van der Veen said 44 people were arrested in total – 28 Celtic fans and 16 followers of Ajax, a club with a notorious hooligan element.

Six Celtic supporters have been accused of violent disorder and will appear before a magistrate today.

Another 12 travelling supporters were released after paying fines of up to €500 each. Ten more were freed with no further action.

Scots police were working with Dutch officers to identify fans from video of the clashes.

It’s understood some of the trouble began when Ajax yobs snatched a flag from Celtic fans.

Riot police soon arrived, and were joined by dozens of cops in plain clothes.

Asked about fans’ complaints that the police were heavy-handed, Mr van der Veen said: “It is hard for me to say anything about that.”

Video footage posted on social networking sites from Celtic and Ajax fans, as well as passers-by, began to provide a clearer picture of the violence.

In one clip, Celtic fans outside a bar were seen in a confrontation with mounted police in a narrow street near Dam Square.

A small number of fans hurled bottles as riot vehicles arrived, then backed off as horses and plain-clothes cops approached.

In another video, Celtic fans were beaten by a group of men, believed to be plain-clothes police, as they were arrested. Later, travelling fans were shown throwing items at a tram and attacking a man on the ground, also thought to be a policeman.

Celtic fan Barry Currier, 40, was arrested for allegedly attacking a cop during the trouble.

His brother Stuart, of Wishaw, Lanarkshire, said he was still being held and had been moved to a larger prison.

Stuart claimed Ajax fans started the trouble in the square, then police tactics made it worse.

He said: “We saw about 20 plain-clothes police charging through the crowd.

“They were just hitting folk, punching guys, then shouting ‘Police! Police!’ I was hit by a policeman on horseback. They were lashing out at everybody.

“It was too heavy-handed. I don’t know why they had the plain-clothes officers running in amongst us.

“Then, obviously, some Celtic fans reacted badly. It was crazy.

“Me and my pal stood in front of this old Dutch couple to protect them. They were terrified.

“Two or three Ajax fans in bars said to us: ‘It is the police that have caused this.’”

Celtic had urged their fans to take care after thugs with pickaxe handles attacked well-behaved visiting supporters in a city centre bar on Tuesday night.

Last night, the club said they were investigating the Dam Square clashes. They said they knew of five fans still in custody – one less than the police figure.

The club added: “We are not clear if they have any formal association with the club. We will be liaising with the Amsterdam authorities, our own police and the British Consulate in order to fully understand events.

“We would stress that there is no excuse for any form of violent conduct.

“In addition, we have received numerous complaints from Celtic supporters in relation to their treatment in Amsterdam, which we will investigate fully.”

The club added: “There is no question that Celtic supporters have been subjected to a high degree of provocation.

“Last week, our supporters were the target of missiles thrown from Ajax supporters at Celtic Park, a night where 300 seats were damaged within the stadium.

“This was followed by an organised attack on a group of Celtic supporters in Amsterdam on Tuesday.

“We have also received numerous individual reports of other attacks on our fans.

“The Celtic travelling support has a magnificent reputation across Europe and our fans have visited major European cities over many years without incident.

“Once again the overwhelming majority of our supporters behaved impeccably.”